How to make physically accurate silver in Cycles?
I have one that uses RGB Curves, here are the coords,there are 4 points in the R,G,B and just 2 in color, hope it helps. If not LUXRENDER.

Red = P1(x 0.0, y .96) P2(x .55, y .96) P3(x .83636, y .95) P4(x 1.0, y 1.0)

Green = P1(x 0.0, y .94) P2(x .5, y .94) P3(x .85091, y .94) P4(x 1.0, y 1.0)

Blue = P1(x 0.0, y .91) P2(x .5, y .91) P3(x .81364, y .92) P4(x 1.0, y 1.0)

Color = P1(x 0.0, y 0.0) P2(x 1.0, y 1.0)